Interfacial Convective Assembly for High Aspect Ratio Structures Without Surface Treatment

ABSTRACT

A method for assembling colloidal particles onto a substrate surface through fluid transport. The method comprises placing a first fluid placed adjacent to the substrate surface, applying a colloidal dispersion on top of the first fluid layer and removal of the first fluid layer. The method is extremely versatile, and is especially useful in depositing colloidal materials in high aspect ratio channels and vias without the need for prior treatment of the surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/702,133, filed on Jul. 15, 2013, which is a U.S. National Phaseof PCT/US2011/039388, filed on Jun. 7, 2011, which claims priority toU.S. Patent Application No. 61/352,523 filed on Jun. 8, 2010, thedisclosures of which are hereby incorporated by reference herein.

GOVERNMENT RIGHTS

The invention was developed with government support from Grant Nos.0425826 and 0832785 from the National Science Foundation. The governmenthas certain rights in the invention.

TECHNICAL FIELD

The present invention relates generally to methods of self-assembly,particularly to self-assembly of component articles, including thosespanning the nanometer to micron range, and more particularly intomicro- and/or nanodimensioned vias and channels of composite articles.

BACKGROUND

Controlling the deposition of nano-dimensioned solids at the nanometerscale has the potential to revolutionize technology through developmentof materials and devices with control of mechanical, optical, electronicand structural properties. Moreover, recent research has led to a hostof new fundamental scientific insights, including controlled nanoscalesynthesis and processing of both organic (soft) and inorganic (hard)material and the development of nano-scale precursors for thesemacroscopic materials and devices. A challenge, therefore, is to developan approach that can combine a variety of organic and inorganic buildingblocks, provide down to nanometer-scale structural control andsimultaneously lead to macroscopic devices or materials in a practicaland cost-effective way. Moreover, the approach must be flexible so thatit can be readily extended to a variety of materials or propertieswithout substantial revision of the entire process. These are demandinggoals that require novel approaches and development of basic science.

Conventional metal deposition methods such as sputtering or evaporationhave poor selectivity, required elevated temperature and need specialvacuum systems. Methods such as dip-coating using colloidal suspensionstake long time and are difficult to apply on thin and bendablesubstrates. Photolithography provides a means of generating structure,generally planar in nature, with a spatial resolution on the nanometerto micron size scale, but this technique is limited to a small set ofmaterials.

Chemical synthesis, for example synthesizing carbon and other nanotubes,can provide molecular resolution, but is limited in its ability toindependently control mechanical, structural, electronic and opticalproperties of a material.

One technique of recent interest involves the selective deposition ofnano- or micro-dimensioned particles by self-assembly. Self-assembly isa term used to define the spontaneous association of entities intostructural aggregates. In particular, molecular self-assembly providesthe basis for a successful strategy for generating large, structuredmolecular aggregates, by the spontaneous association of molecules. See,for example, Whitesides, et al., in “Noncovalent Synthesis: UsingPhysical-organic Chemistry to Make Aggregates”, Accts. Chem. Res., 28,37-44 (1995); Whitesides, G. M., “Self-Assembling Materials”, ScientificAmerican, 273, 146-149 (1995); Philip, et al., Angew. Chem., Int. Ed.Engl., 35, 1155-1196 (1996).

Self-assembly of molecules can be made to occur spontaneously atliquid/gas, liquid/liquid, or solid/liquid interfaces to formself-assembled monolayers of the molecules when the molecules have ashape that facilitates ordered stacking in the plane of the interfaceand each includes a chemical functionality that adheres to the surfaceor in another way promotes arrangement of the molecules with thefunctionality positioned adjacent the surface. U.S. Pat. No. 5,512,131,and U.S. patent application Ser. Nos. 08/695,537, 08/616,929,08/676,951, and 08/677,309, and International Patent Publication No. WO96/29629, all commonly-ownled, describe a variety of techniques forarranging patterns of self-assembled monolayers at surfaces for avariety of purposes.

Much of the literature in this area describes the self-assembly offorming extended colloidal structures, but several techniques aredescribed for forming such nano- and microscale patterning, includingtethering colloidal gold nanoparticles to surfaces with thiol groups(Mirkin, et al., A DNA-Based Method for Rationally AssemblingNanoparticles Into Macroscopic Materials, Nature, 382, (Aug. 15, 1996)).

The concept of using capillary action to deposit colloid ornano-materials has been described as useful in providing patternedself-assembled arrays. Yamaki, et al., in “Size Dependent Separation ofColloidal Particles in Two-Dimensional Convective Self-Assembly”Langmuir, 11, 2975-2978 (1995), relies on lateral capillary force andconvective flow to provide “convective self-assembly” of colloidalparticles ranging in size from 12 nm to 144 nm in diameter in a wettingliquid film on a mercury surface. Cralchevski, et al., in “CapillaryForces Between Colloidal Particles” Langmuir, 10, 23-36 (1994), describecapillary interactions occurring between particles protruding from aliquid film due to the capillary rise of liquid along the surface ofeach particle.

Shi-Kai Wu, et al., “Self Assembly of Polystyrene Microspheres WithinSpatially Confined Rectangular Microgrooves,” J Mall. Sci., 43 (19),6453-6458 (2008) describes the use of capillary action to self-assemble262 to 1000 nm polystyrene spheres onto patterned silicon wafers withone-dimensional microgrooves of different widths (0.76-6 microns).Processing variables including evaporation temperature, particle size,groove width, and groove height were examined to explain the results.

0-0k Park, el al., “Method for Manufacturing Colloidal Crystals ViaConfined Convective Assembly,” U.S. Pat. No. 7,520,933, issued Apr. 21,2009, discloses methods of manufacturing colloidal crystals using aconfined convective assembly, comprising infusing colloidal suspensionbetween two substrates and self-assembling the particles by capillaryaction. Substrates may include glass, inorganic and organic polymers;particles may include high molecular weight polymers, inorganicpolymers, metals, and metal oxides. Solvents useful for the convectivetransfer include water and alcohol.

Peng Jiang, et al., “Polymers Having Ordered Monodisperse Pores andTheir Corresponding Ordered, Monodisperse Colloids,” U.S. Pat. No.6,929,764 (issued Aug. 16, 2005) describes the deposition of nano-silica“according to an appropriate technique, such as . . . convectiveself-assembly method.”

U.S. Pat. No. 5,45,291 (Smith) describes assembly of solidmicrostructures in an ordered manner onto a substrate through fluidtransfer. The microstructures are shaped blocks that, when transferredin a fluid slurry poured onto the top surface of a substrate havingrecessed regions that match the shapes of the blocks, insert into therecessed regions via gravity. U.S. Pat. No. 5,355,577 (Cohn) describes amethod of assembling discrete microelectronic or micro-mechanicaldevices by positioning the devices on a template, vibrating the templateand causing the devices to move into apertures. The shape of eachaperture determines the number, orientation, and type of device that ittraps.

Self-assembly on patterned surfaces is particularly useful as a way ofmaking nano- and microscale devices, for example electronic andelectrochemical systems, sensors, photonic devices, biosensors anddevices, information storage medium, display devices and opticaldevices, and medical (e.g., drug release) devices.

However, when attempting to apply convective self-assembly, severalproblems become evident. These particular problems include difficultiesin depositing colloidal particles into high aspect ratio trenches orwells.

The main problem in hydrophobic structures with high aspect ratio isthat water cannot penetrate and touch the bottom surface, so it isimpossible to use liquid assembly techniques as dip-coating orconvective assembly. Conventional plastic substrates show water contactangles around 100° and they are usually reduced applying 0₂ plasma or UVradiation to make the surface hydrophilic (contact angle below 20°).This problem is exacerbated in high aspect ratio nanostructures showedsuper-hydrophobicity (130°) before applying 0₂ plasma and a high contactangle (90°) after the plasma was applied. Also, 0₂ plasma is known todestroy or erode plastic patterns.

Another problem is that plastic substrates are usually thin and easy tobend and it is difficult to make conformal assembly at large areas.

Still another problem is that the time necessary for particles to movefrom, typically, aqueous dispersions into high aspect ratio features(e.g., vias and trenches) tends to be long. All of these problems becomeincreasingly acute as the dimensions of the vias and trenches shrink,and are especially problematic for nano-dimensioned features.

What is needed is a versatile technique for facilitating convectiveself-assembly that accommodates a wide range of nano- or microparticles,works quickly over large areas, when the particles (or other nano- ormicro-building blocks) have to be assembled into deep trenches or vias,whether the surface is hydrophobic or hydrophilic, without surfacetreatment.

SUMMARY

The present invention is directed to a method of facilitating convectiveself-assembly that accommodates a wide range of colloidal particles,works quickly over large areas, when the colloidal particles (or othernano- or micro-dimensioned building blocks) have to be assembled intodeep channels, holes, wells, or vias, whether the surface is hydrophobicor hydrophilic, without the need for high vacuum or surface treatment.As such, the various embodiments described herein provide a flexible andcost effective approach to achieving its intended purpose.

One embodiment of this invention is a method for depositing colloidalparticles onto a substrate surface comprising: (a) providing a substratehaving a surface; (b) depositing a first layer of a first fluid onto thesurface of the substrate; and (c) depositing a second layer of anaqueous dispersion of colloidal particles on top of the first layer ofthe first fluid; and (e) removing the first layer of the first fluid.This process results in the colloidal particles forming a layer on thesurface of the substrate, either over the entire substrate or overportions of the substrate. Additional and separate additive embodimentsinclude this first embodiment plus either (d) optionally covering thesecond layer with a cover so as to forming an assembly comprising asandwich of the first and second layers between the substrate and thecover or (f) removing the water from the second layer of the aqueousdispersion, leaving a layer of particles on the surface of thesubstrate, or both (d) and (t).

The method is flexible in that is allows that the surface of thesubstrate can be either hydrophobic or hydrophilic, or may comprisesections which are both hydrophobic and hydrophilic. Further, thesubstrate may be flat or curved, may be flexible or rigid, or comprise ashape memory material. The substrate may comprise a bulk material or atleast a partial surface coating comprising one or more glass, organicpolymer, inorganic polymer, ceramic, metal, or metalloid, or an area orlayered combination or mixture thereof.

The invention teaches that the substrate may contain patterned featureswhich either protrude or contain recesses or indentations (e.g.,channels, trenches, and/or holes, wells, or vias).

Certain embodiments provide that the substrate comprises insulative,conductive, or semi-conductive materials. Within these categories, thesubstrate may comprise one or more glass, inorganic or organic polymers,crystalline or polycrystalline ceramic, metal, or metalloid. Thesubstrate surface comprises patterned micro- and/or nano-dimensionedfeatures. Such micro- and/or nano-dimensioned features include channelsor trenches or holes, wells, or vias which may be formed into thesubstrate or by protruding surfaces. These surfaces may or may not beused in combination with some form of chemical or physical etching.

In other separate embodiments, the first layer of a first fluid and thesecond layer of the aqueous dispersion may be applied by spin-, dip-,brush-, or spray-coating, or by the application of a droplet usingmethods known to those skilled in the art.

In combination with any of the preceding or succeeding embodiments,various embodiments of the method provides that the first fluid wets thesubstrate. Such embodiments can be accomplished with fluids comprisingone or more of various organic liquids, for example alcohols, aromatics,amines, esters, hydrocarbons, or ketones, or mixtures thereof.Isopropanol is a particularly well suited organic fluid to be used inthis invention.

The physical properties of boiling point (or more generally, the vaporpressure at the then ambient temperature), the viscosity, specificgravity, and the surface tension of the first fluid all impact theefficiency of the method. In certain embodiments, this first fluid maybe immiscible, partially miscible, or completely miscible with waterand/or the aqueous dispersions of the colloidal particles.

The aqueous layer comprises water and colloidal particles, and mayinclude other materials including surfactants, colorants, fluorescents,markers, preservatives, and/or soluble dopants depending on the finalapplication. Virtually any potentially available secondary material canbe used, provided they do not substantively interfere with the abilityof the layer to deliver and deposit the colloidal particles to thesurface of the substrate.

The first layer may be removed using several techniques, including bythe application of heat or vacuum or both. In such cases, the firstlayer may be removed by some contribution of evaporation or comminglingwith, and incorporating into, the aqueous phase, or both. Once the firstfluid is removed, and the colloidal particles are deposited, theinvention describes that the liquid portion of the aqueous dispersion isremoved by the application of heat or vacuum or both. Generally, theapplication of heat is referring to temperatures of about 80° C. orless, about 60° C. or less, about 40° C. or less, or so-call roomambient temperatures (e.g., ca. 2025° C.). The skilled artisan willappreciate that higher temperatures will cause faster evaporation,though the speed of evaporation is balanced against the homogeneityand/or selectivity he or she wishes to attain.

It should be appreciated that articles produced by these methods arealso within the scope of this invention. Such articles include, forexample, chemical, biochemical, electrical, electromagnetic field orfrequency sensors, information storage media, energy storage units,energy conversion cells, display devices, or video or optical devices.More complicated systems are also contemplated herein, includingchemical, biochemical, electrical, or electromagnetic field or frequencysensing systems, information transfer or communication systems, energystorage or conversion systems, or video or optical communication systemscomprising a device made by these methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a substrate containing patterned features; when madeof polyethylene, it also represents a super-hydrophobic structure.

FIG. 2 is a schematic illustration of one embodiment of the inventiveprocedure.

FIG. 3 is a numerical simulation of convective flow between twodifferent layers at room temperature.

FIG. 4 provides fluorescent microscope images of selective assemblyusing 22 nm PSL particles. In this case, the substrate is polyethylene,which is highly hydrophobic, exhibiting a contact angle of 110-130°.FIG. 4A shows the substrate before assembly. FIG. 4B shows that largearea after assembly. FIG. 4C shows a bended area after assembly. FIG. 4Dshows the assembly at high magnification.

FIG. 5 shows 5 nm gold particles assembled in 300 nm trenches (FIG.5(A)) and 50 nm gold particles assembled in 300 nm vias (FIG. 5(B)).

FIG. 6 provides SEM images of selective assembly using 5 and 50 nm goldparticles in 200 and 300 nm vias and trenches. In this case, thesubstrate is PMMA, which is hydrophobic, exhibiting a contact angle ofapproximately 70.

FIG. 7 provides images of selective assembly using 50 nm PSL particles.In this case, the substrate is SiO₂, which is hydrophilic, exhibiting acontact angle of less than 20. FIG. 7(A) is a fluorescent microscopeimage, and FIG. 7(B) is an SEM image

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention is directed to a method of facilitating convectiveself-assembly that accommodates a wide range of colloidal particles,works quickly over large areas, when the colloidal particles (or othernano- or micro-dimensioned building blocks) have to be assembled intodeep channels, holes, wells, or vias, whether the surface is hydrophobicor hydrophilic, without the need for high vacuum or surface treatment.As such, the various embodiments described herein provide a flexible andcost effective approach to achieving its intended purpose.

The present invention may be understood more readily by reference to thefollowing detailed description taken in connection with the accompanyingFigures and Examples, which form a part of this disclosure. It is to beunderstood that this invention is not limited to the specific products,methods, conditions or parameters described and/or shown herein, andthat the terminology used herein is for the purpose of describingparticular embodiments by way of example only and is not intended to belimiting of any claimed invention. Similarly, any description as to apossible mechanism or mode of action or reason for improvement is meantto be illustrative only, and the invention herein is not to beconstrained by the correctness or incorrectness of any such suggestedmechanism or mode of action or reason for improvement. Throughout thistext, it is recognized that the descriptions refer both to the method ofpreparing such devices and to the resulting, corresponding physicaldevices themselves, as well as the referenced and readily apparentapplications for such devices.

In the present disclosure the singular forms “a,” “an,” and “the”include the plural reference, and reference to a particular numericalvalue includes at least that particular value, unless the contextclearly indicates otherwise. Thus, for example, a reference to “amaterial” is a reference to at least one of such materials andequivalents thereof known to those skilled in the art, and so forth.

When values are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms anotherembodiment. In general, use of the term “about” indicates approximationsthat can vary depending on the desired properties sought to be obtainedby the disclosed subject matter and is to be interpreted in the specificcontext in which it is used, based on its function, and the personskilled in the art will be able to interpret it as such. In some cases,the number of significant figures used for a particular value may be onenon-limiting method of determining the extent of the word “about.” Inother cases, the gradations used in a series of values may be used todetermine the intended range available to the term “about” for eachvalue. Where present, all ranges are inclusive and combinable.

It is to be appreciated that certain features of the invention whichare, for clarity, described herein in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the invention that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges include each and every value within that range.

Generally terms are to be given their plain and ordinary meaning such asunderstood by those skilled in the art, in the context in which theyarise. To avoid any ambiguity, however, several terms are describedherein.

One embodiment of this invention is a method for depositing colloidalparticles onto a substrate surface comprising: (a) providing a substratehaving a surface; (b) depositing a first layer of a first fluid onto thesurface of the substrate; and (c) depositing a second layer of anaqueous dispersion of colloidal particles on top of the first layer ofthe first fluid; and (e) removing the first layer of the first fluid.This process results in the colloidal particles forming a layer on thesurface of the substrate, either over the entire substrate or overportions of the substrate. Additional and separate additive embodimentsinclude this first embodiment plus either (d) optionally covering thesecond layer with a cover so as to forming an assembly comprising asandwich of the first and second layers between the substrate and thecover or (f) removing the water from the second layer of the aqueousdispersion, leaving a layer of particles on the surface of thesubstrate, or both (d) and (t).

These steps are shown schematically in FIGS. 1 and 2. FIG. 1 shows asubstrate containing patterned channels. A cross-sectional view of asimilar configuration is shown in FIG. 2A, showing a pattern having highaspect ratio channels 20 having been applied to a glass substrate 21. InFIG. 2B, a layer of the first fluid 22 is applied to the pattern. InFIG. 2C, a layer of aqueous colloidal material 23 is applied on top ofthis first layer, and in FIG. 2D an optional cover plate 24 is placed ontop of the aqueous colloidal layer 23, to provide conformal water filmthickness. In the particular embodiment shown in FIG. 2E, heat isapplied to accelerate the mass exchanges between the two layers usinginterfacial convection, and in FIG. 2F, both fluid layers have beenremoved, leaving behind deposited colloidal particles 25.

FIG. 3 shows a numerical simulation of convective flow between the firstlayer of first fluid and the water of the aqueous colloidal layer.

FIG. 4 shows fluorescent microscope images of selective self assemblyusing 22 nm polystyrene latex (PSL) particles. Of particular interest,FIG. 4D shows the selectivity of the deposition relative to the entiresurface.

It should also be appreciated that any of the embodiments describedherein may be employed more than once to the same substrate, either indifferent or over the same areas of the substrate, such that thesubstrate may ultimately comprise multiple layers of colloidalparticles, such that these particle layers may or may not overlap one ormore preceding layer, and the individual layers may comprise the same ordifferent materials.

As used herein, the term “nano-” as in “nano-dimensioned,” “nano-scale,”or “nano-structured” refers to a dimension, scale, or structure havingat least one dimension in the range of 0.5 to about 1000 nm, preferablyin the range of about 1 to about 500 nm, more preferably in the range ofabout 5 to about 350 nm, more preferably in the range of about 5 toabout 250 nm, still more preferably in the range of about 10 to about100 nm; i.e., having a dimension in the range independently bounded atthe lower end by about 0.5, 1, 5, 10, 15, 20, 25, 50, 75, 100, 250, or500 nm and at the upper end by about 1000, 750, 500, 350, 250, 150, 100,50, 25, and 10 nm. Non-limiting exemplary ranges, for example, includethose in the range of about 5 to about 50 nm, about 50 to about 100 nm,about 100 to about 350 nm, about 75 to about 500 nm, or about 500 toabout 1000 nm. When the terms “nano-channel” or “nano-trench” is usedherein, these nano-dimensions refer at least to the width of said“nano-channel” or “nano-trench.”

As used herein, the term “micro-” as in “micro-dimensioned,”“micro-scale,” or “micro-structured” refers to a dimension, scale, orstructure having at least one dimension in the range of about 0.5 toabout 1000 micron, preferably in the range of about 1 to about 500micron, more preferably in the range of about 5 to about 350 micron,more preferably in the range of about 5 to about 250 micron, still morepreferably in the range of about 10 to about 100 micron; i.e., having adimension in the range independently bounded at the lower end by about0.5, 1, 5, 10, 15, 20, 25, 50, 75, 100, 250, or 500 micron and at theupper end by about 1000, 750, 500, 350, 250, 150, 100, 50, 25, and 10micron. Non-limiting exemplary ranges, for example, include those in therange of about 1 to about 5 micron, about 5 to about 50 micron, about 50to about 100 micron, about 100 to about 350 micron, about 75 to about500 micron, or about 500 to about 1000 microns. When the terms“micro-channel” or “micro-trench” is used herein, these micro-dimensionsrefer at least to the width of said “micro-channel” or “micro-trench.”

As used herein, the term “colloidal” refers to separate embodimentsindependently comprising either micro- or nano-dimensioned particles orboth micro- and nano-dimensioned particles.

The method is flexible in that is allows that the surface of thesubstrate can be either hydrophobic or hydrophilic, or may comprisesections which are both hydrophobic and hydrophilic. The method isespecially discriminating on hydrophobic substrates, especially thosecontaining hydrophobic channels, trenches, holes, wells, or vias. Thatis, when hydrophilic substrates are subjected to the methods describedherein, colloidal materials tend to distribute over much of the entiresurface, including within the channels, trenches, holes, wells, or vias,whereas when hydrophobic substrates are subjected to the methodsdescribed herein, colloidal materials tend more to aggregate more withinthe channels, trenches, holes, wells, or vias, and less over the largerhydrophobic surfaces.

Further, the substrate may be flat or curved, may be flexible or rigid,or comprise a shape memory material. The substrate may comprise a bulkmaterial or at least a partial surface coating comprising one or moreglass, organic polymer, inorganic polymer, ceramic, metal, or metalloid,or an area or layered combination or mixture thereof. As used herein,the phrase “combination or mixture thereof” is intended to reflectembodiments comprising layered structures of the preceding materials, aswell as homogeneous or heterogeneous mixtures of the preceding materialsand combinations of layered homogeneous or heterogeneous materials. Thatis, different areas of the substrate may comprise different materials ormixtures of materials (e.g., where the substrate is a composite ofseveral materials) and/or may comprise layers of different materials,such that one or more of the different materials may be exposed to theenvironment.

The invention teaches that the substrate may contain patterned featureswhich either protrude or contain recesses or indentations (e.g.,channels, trenches, and/or holes, wells, or vias). The terms “channels”and “trenches” carry the same meaning, recognized by those skilled inthe art, and may be used interchangeably herein. Similarly, the terms“holes,” “wells,” and “vias” are intended to reflect recessed orindented features whose presented surface geometry is approximately thatof a circle or regular polygon. These patterned features may belithographically patterned and/or may be provided by other standardsemiconductor processing techniques, such as masking, sputtering,chemical vapor deposition, sol-gel processing, plasma deposition oretching, drilling, micromachining, or any combination of thesetechniques. For example, in but one non-limiting example, the substratemay comprise lithographically patterned sputtered metallic conductors.

Certain embodiments provide that the substrate comprises insulative,conductive, or semi-conductive materials.

The substrate and/or surface may include one or more glass comprising asilicate, borate, or phosphate, or combination or mixture thereof.Inorganic polymers or precursors similarly may include polysiloxanes,including polydimethylsiloxanes, silicates or aluminosilicates, or acombination or mixture thereof.

Other embodiments provide that the substrate and/or surface comprises atleast one organic polymer, which may include at least one thermoplasticor thermoset resin or copolymer or mixture thereof. Representativepolymers which may be applied include those comprising at least onepartially or perfluorinated polymer, a polycarbonate, a polyester, apolyalkylene, a polyacrylate or a polymethacrylate, a polystyrene, or apolyacrylonitrile, or a copolymer, combination, or mixture thereof. Theorganic polymers can be electrically conductive or semiconductive.Non-limiting examples of such materials include polymers comprising apoly(para-phenylene vinylene), polythiophene, poly(paraphenylene),polyquinoline, polypyrrole, polyacetylene, or polyfluorene, or acopolymer or mixture thereof.

As described herein, the various polymers may comprise materials whichare natural, synthetic, biocompatible, biodegradable, non-biodegradable,and/or biosorbable. Unless specifically restricted to one or more ofthese categories, the polymers may comprise materials from any one ofthese categories. To be implantable, such as may be required forbiosensors, for example, such embodiments provide that the materialsused are at least biocompatible, and preferable approved by the UnitedStates Food and Drug Administration in the United States (or acorresponding regulatory agency in other countries).

The phrase “synthetic polymer” refers to polymers that are not found innature, even if the polymers are made from naturally occurringbiomaterials. Examples include, but are not limited to, aliphaticpolyesters, poly(amino acids), copoly(ether-esters), polyalkylenesoxalates, polyamides, tyrosine derived polycarbonates,poly(iminocarbonates), polyorthoesters, polyoxaesters, polyamidoesters,polyoxaesters containing amine groups, poly(anhydrides),polyphosphazenes, polysiloxanes, and combinations thereof.

The phrase “biocompatible polymer” refers to any polymer (synthetic ornatural) which when in contact with cells, tissues or body orphysiological fluid of an organism does not induce adverse effects suchas immunological reactions and/or rejections and the like. It will beappreciated that a biocompatible polymer can also be a biodegradablepolymer.

The phrase “biodegradable polymer” refers to a synthetic or naturalpolymer which can be degraded (i.e., broken down) in the physiologicalenvironment such as by enzymes, microbes, or proteins. Biodegradabilitydepends on the availability of degradation substrates (i.e., biologicalmaterials or portion thereof which are part of the polymer), thepresence of biodegrading materials (e.g., microorganisms, enzymes,proteins) and the availability of oxygen (for aerobic organisms,microorganisms or portions thereof), carbon dioxide (for anaerobicorganisms, microorganisms or portions thereof) and/or other nutrients.Aliphatic polyesters, poly(amino acids), polyalkylene oxalates,polyamides, polyamido esters, poly(anhydrides), poly(beta-amino esters),polycarbonates, polyethers, polyorthoesters, polyphosphazenes, andcombinations thereof are considered biodegradable. More specificexamples of biodegradable polymers include, but are not limited to,collagen (e.g., Collagen I or IV), fibrin, hyaluronic acid, polylacticacid (PLA), polyglycolic acid (PGA), polycaprolactone (PCL),poly(Lactide-co-Glycolide) (PLGA), polydioxanone (PDO), trimethylenecarbonate (TMC), polyethyleneglycol (PEG), Collagen, PEG-DMA, alginateor alginic acid, chitosan polymers, or copolymers or mixtures thereof.

The phrase “non-biodegradable polymer” refers to a synthetic or naturalpolymer which is not degraded (i.e., broken down) in the physiologicalenvironment. Examples of non-biodegradable polymers include, but are notlimited to, carbon, nylon, silicon, polyurethanes, polycarbonates,polyacrylonitriles, polyanilines, polyvinyl carbazoles, polyvinylchlorides, polyvinyl fluorides, polyvinyl imidazoles, polyvinylalcohols, polystyrenes and poly(vinyl phenols), aliphatic polyesters,polyacrylates, polymethacrylates, acyl-substituted cellulose acetates,nonbiodegradable polyurethanes, polystyrenes, chlorosulphonatedpolyolefins, polyethylene oxides, polytetrafluoroethylenes,polydialkylsiloxanes, and shape-memory materials such as poly(styrene-block-butadiene), copolymers or mixtures thereof.

Crystalline or polycrystalline ceramic composites may be used assubstrates and/or surface coatings where the ceramic comprises a metalor metalloid oxide, nitride, or carbide, or a combination or mixturethereof. Such ceramic compositions may include binary, ternary,quaternary carbide, nitride, or oxide compositions. Non-limitingexamples include oxides of aluminum, antimony, calcium, indium, iron,magnesium nickel, silicon, tin, titanium, zinc, or zirconium; nitridesof aluminum, boron, carbon, silicon, or titanium; and/or carbides ofaluminum, boron silicon, or titanium, or solid solutions or mixturesthereof.

In separate embodiments, the conductive materials may comprise metals,including, but not limited to aluminum, gold, silver, platinum, cadmium,copper, nickel, titanium, or iron, or a combination or mixture thereof.

The substrate and/or surface may also comprise metalloid comprisingconducting, semi-conducting, or insulating, doped or undoped Si, CdS,CdSe, Ge, GaAs, GaAlAs, ZnS, InP, or Ge, or a combination or mixturethereof.

Silica, glass, polyethylene, or polycarbonate are preferred substratesfor these methods.

The methods of the invention further provides embodiments wherein thesubstrate surface comprises patterned micro- and/or nano-dimensionedfeatures. Such micro- and/or nano-dimensioned features include channelsor trenches or holes, wells, or vias which may be formed into thesubstrate or by protruding surfaces. In one non-limiting example, a 10nm channel may be formed by lithographically etching it into thesubstrate surface or by forming protruding structures separated by thisdistance. The skilled artisan is familiar with the means to form suchstructures. Preferred embodiments include those where the channel widthor hole diameter has dimensions on the order of about 5 nm to 1000microns, preferably about 10 nm to about 500 nm, more preferably about50 to about 300 nm, and still more preferably about 100 to about 300 nm,but the full scope of these allowable dimensions is as defined above fornano- and micro-dimensioned features.

The invention is particularly attractive when these channels have aspectratios of about 10 or more, where aspect ratio is defined to be theratio of height to width of the channel or the ratio of height to thecross-sectional distance of the hole, well, or via. However, the methodis not limited to aspect ratios of this dimension and also includesembodiments where the aspect ratio is about 0.5 or more, about 1 ormore, about 2 or more, about 5 or more, about 50 or more, about 75 ormore, or about 100 or more. Similarly the ratio of the dimension of thecolloidal particle to the width of the channel is important, but themethod provides flexibility here as well. In order for the method toprovide deposition of the colloidal particle within the channel, theratio of the channel width to particle size obviously must be at leastone, preferably greater than about 2, more preferably greater than about5, more preferably greater than about 10, more preferably greater thanabout 20, and still more preferably greater than about 50.

While many of the various embodiments do not include the use of chemicalor physical etching to improve the wetting of the substrate surface,many other embodiments provide that such chemical or physical etching beused. In these embodiments, etching can be accomplished by plasma or wetchemical etching, or physical abrasive techniques.

Moving beyond the embodiments related to the substrate, in otherseparate embodiments, the first layer of a first fluid and the secondlayer of the aqueous dispersion may be applied by spin-, dip-, brush-,or spray-coating, or by the application of a droplet using methods knownto those skilled in the art.

In combination with any of the preceding or succeeding embodiments,various embodiments of the method provides that the first fluid wets thesubstrate. In the context of this specification, “wetting” is intendedto reflect that the contact angle of the fluid with the substratematerial is less than the contact angle of water with the same substratematerial. Such embodiments can be accomplished with fluids comprisingone or more of various organic liquids, for example alcohols, aromatics,amines, esters, hydrocarbons, or ketones. Preferred embodiments of thisinvention tend to be alcohols, esters, and ketones, especially where thenormal boiling point is less than that of water. While obviously, for agiven class of organic materials, this boiling point limit depends on avariety of parameters, including, for example, degree of hydrogenbonding, specific geometry, and number and position of double bonds, theskilled artisan would appreciate that generally this refers topreferably C1_5 alcohols, ketones, esters, more preferably C1-4alcohols, C1_6 ketones and esters, and still more preferably C1-3alcohols, acetone, and ethyl acetate. Isopropanol is a particularly wellsuited organic fluid to be used in this invention.

The most preferred embodiments of the present invention tend to be thesetypes of chemicals, because of the physical characteristics which theyexhibit. Without intending to be bound by any particular theory, it isbelieved that the use of organic fluids as described herein works isthat the first fluid wets the narrow, high aspect ratio channels orfeatures more efficiently than does water. When subjected to heat orvacuum, the first fluid is removed, either by evaporation from beneathor dissolution or commingling in the water or both, depending on themiscibility of the first fluid with water. Once the first fluid isremoved, the aqueous dispersion can more efficiently and quickly occupythe space left by the removed first fluid within the narrow channels orfeatures, thereby accelerating the deposition of the dispersed colloidaldimensioned materials. Under this model, the physical properties ofboiling point (or more generally, the vapor pressure at the then ambienttemperature), the viscosity, and the surface tension of the first fluidall impact the efficiency of the method. It is also determined that thedensity of the first fluid relative to that of water is important, themethod improving as the density of the first fluid decreases, relativeto that of water, such that the density difference is increased. Certainembodiments, then, provide that the specific gravity of the first fluidbe in the range of about 0.5 to about 1.1, in the range of about 0.6 toabout 0.95, more preferably in the range of about 0.6 to about 0.85,more preferably in the range of about 0.6 to about 0.75, and morepreferably in the range of about 0.6 to about 0.65, where specificgravity is defined as the ratio of the density of the fluid, typicallyat 25° C. to that of water, when measured at 4° C.

In certain embodiments, this first fluid may be immiscible, partiallymiscible, or completely miscible with water and/or the aqueousdispersions of the colloidal particles. The term “immiscible” as usedherein, refers to a fluid exhibiting a mutual solubility with water at25° C. of less than about 5%. “Partially miscible” is defined asexhibiting a mutual solubility with water at 25° C. in the range ofabout 5 to about 95%, and “completely miscible” refers to liquids whichexhibit mutual solubility with water at 25° C. of more than about 95%.

As applied to vapor pressure, a convenient (if not surrogate) measure isthe normal boiling point (i.e., the boiling point at one atmosphere) isan important property of the first fluid. In certain embodiments, thenormal boiling point of the first fluid is about 99° C. or less, about80° C. or less, more preferably about 60° C. or less, more preferablyabout 50° C. or less, still more preferably about 40° C. or less.

As applied to viscosity, certain embodiments provide that the viscosityof the first fluid be about 2 centipoise or less, at 25° C., morepreferably about 1 centipoise or less, still more preferably about 0.5centipoise or less, at 25° C.

With respect to surface tension, certain embodiments provide that thesurface tension at 25° C. be about 40 dyne/cm or less, more preferablyabout 25 dyne/cm or less, and still more preferably in the range ofabout 20 to about 25 dyne/cm.

The more preferable embodiments for the first fluid exhibit thecombination of properties characterized above as more or most preferableembodiments of the respective property. For example, one such categorywould include those fluids having specific gravities of about 0.85 orless, surface tensions of about 25 dyne/cm or less, and normal boilingpoints of about 85° C. or less.

The attached Table provides characteristic values for these parameters,for selected solvents. While not intended to be limiting, the Tableprovides allows the skilled artisan to select a first fluid with thebalance of properties appropriate for his or her conditions.

Surface Normal Temp. at Viscosity at Tension Boiling which 400 25° C.Specific (dyn/cm) Point, mm Hg (centipoise) Gravity Acetone 23.3 56.3  39.5 0.316 0.792 Acetonitrilc 19.1 81.6   62.5 0.345 0.786 Benzene28.9 80.1 61 0.652 (20° C.) 0.879 tert-Butanol 23.6 82.5 68 2.54  0.779n-Butyl Chloride 23.8 77.8 59 0.469 (15° C.) 0.887 Carbon 27.0 76.7 580.969 (20° C.) 1.595 Chloroform 27.2 61.2 43 0.542 1.489 Cyclohexane25.0 80.7 61  1.02 (17° C.) 0.779 Cyclopentane 22.4 49.3 31 0.493 (14°C.) 0.745 Dichloromethane 28.1 39.8 24 0.449 (15° C.) 1.336 DiethylEther 17.1 34.6 18 0.222 0.708 Ethanol 22.3 78.3 64 1.200 (20° C.) 0.789Ethyl Acetate 23.7 77.1 59 0.441 0.901 Ethylene Dichloride 32.2 83.5 64 0.79 (20° C.) 1.256 Heptane 20.3 98.4 78 0.386 0.684 Hexane 17.9 68.750 0.294 0.659 Methanol 22.6 64.7 50 0.547 0.792 Methyl Ethyl 24.079.6 * 0.426 (20° C.) 0.805 Methyl t-Butyl 19.4 55.2 * 0.36  0.740iso-Propyl Alcohol 21.8 82.3 68 1.96  0.789 n-Propyl Alcohol 23.7 97.282 2.256 (20° C.) 0.804 Pentane 15.5 36.1 19 0.24  0.630 Tetrahydrofuran26.4 66 * 0.48  0.888 Triethylamine 20.7 89 * 0.363 0.729 Water 72.8 10083 0.890 1.000 Values for these properties taken from various sourcesincluding R. H. Perry and C. H. Chilton, Chemical Engineers' Handbook,5th Edition, McGraw-Hill, 1973 and Handbook of Chemistry and Physics,CRC Press, 1982.

As with many of the other parameters, the invention is flexible in itschoice of colloidal particles, both size and composition. While theterms “colloidal” has been used to describe “micro-” and/or “nano-”dimensioned particles, with the terms “micro-” and “nano-” having beendescribed above, the colloidal particles may also be characterized interms of aspect ratio—i.e., the ratio of the longest to shortestdimension. While there is no a priori limit to the aspect ratio for thepresent invention, preferred embodiments, particularly for those caseswhere the skilled artisan is depositing these colloidal particles inhigh aspect ratio channels or holes, are those where the particle aspectratio is less than about 100, less than about 10, less than about 2, orspherical or near spherical.

These colloidal particles may comprise at least one allotrope of carbon,a glass, organic polymer, bioactive material, magnetic material,inorganic materials, ceramic, inorganic salt, metal or metalloid, or acombination or mixture thereof. The types of glasses, organic andinorganic polymers, ceramics, metals, and metalloids may be the samematerials as described above in the context of the substrates.Additionally, inorganic salts may include photonic or similar materials,for example including CdS or AgCl. Allotropes of carbon, inorganicmaterials, metals, metalloids include carbon or inorganic nanotubes,graphenes, fullerenes, or functionalized/addivated version thereof, saidnanotubes defined herein to include single-walled nanotubes,multi-walled nanotubes. In addition to the organic materials describedabove, the colloidal particles may also comprise at least onebiopolymer, said biopolymer including peptides, nucleotides, orpolynucleotides. The term “bioactive material” refers to a materialcapable of eliciting a pharmacological response in a patient.

The particles may comprise crystalline, non-crystalline (amorphous), ora mixture of crystalline and non-crystalline materials. Particles may becharged or uncharged.

The colloidal particles may include single materials or multiplematerials. In the latter case, the particles may comprise compositeswherein one component is intimately mixed with one or more differentmaterials, wherein one component is intimately mixed with a differentphysical form of the same material (such as where a microcrystallineform of a material is homogeneously or heterogeneously contained withinan amorphous form of the same material), wherein multiple material orforms of materials are arranged in layers, or combinations thereof.Included in such arrangements are those embodiments wherein, forexample, optionally coated nanotubes contain fill materials, such asfunctionalized, unfunctionalized, substituted, and/or unsubstitutedfullerenes, metallocenes, organic polymers, inorganic molecules,polymers, or salts, metal or metalloid, metallic cluster, molecularcluster, semiconducting cluster, semi-metallic cluster, or insulatingcluster.electron donor or acceptor to said nanotube, or a moleculeneutral to said nanotube or a mixture thereof.

Provided the dispersion remains fluid, there is no specific limit to theloading of the colloidal particles within the aqueous second layer.Preferably, the aqueous dispersion comprises particles in the range ofabout 0.1 to about 25% by weight relative to the weight of the entireaqueous dispersion, though various separate embodiments of thisinvention also provide that dispersions may include those containing inthe range of about 0.1 to about 90 wt %, about 0.1 to about 50%, about0.1 to about 25%, about 0.1 to about 20%, about 0.1 to about 15%, about0.1 to about 10%, about 0.1 to about 5% by weight, or in the range ofabout 1 to about 90 wt %, about 1 to about 50%, about 1 to about 25%,about 1 to about 20%, about 1 to about 15%, about 1 to about 10%, about1 to about 5% by weight, or in the range of about 5 to about 10%, about10 to about 20%, about 20 to about 30%, about 30 to about 40%, about 40to about 50%, or about 50 to about 60% by weight relative to the weightof the entire aqueous dispersion, again provided the dispersion remainsfluid. The skilled artisan is well able to determine optimal loadings ofthe aqueous dispersion: at higher loadings, the channels, trenches,holes, wells, or vias tend to fill preferentially to the whole surface.

In still other embodiments, the aqueous dispersion further comprises aninternally dispersed phase of a partially immiscible or immiscibleliquid, these terms having been defined above, wherein some portion ofthe colloidal particles is positioned within the internally dispersedliquid phase. Separate embodiments also provide that some portion of thecolloidal particles are positioned at the interface between the aqueousand the internally dispersed liquid phase. As used herein, “some of isgiven its common meaning, that being “less than all.” More specificembodiments describe the situation where the portion of the colloidalparticles positioned within or at the interface of the between theaqueous and the internally dispersed liquid phase is about 10%, about20%, about 30%, about 40%, about 50%, about 60%, about 70%, about 80%,about 90%, or more, by weight relative to the weight of the entireaqueous dispersion.

The invention also teaches that other embodiments of the method includethose wherein the colloidal particles further comprise a ligand orsurfactant. These ligands or surfactants may be chemically bonded,electrostatically attached, or physically entangled with the colloidalparticles.

The optional cover plate has several effects on the methods describedherein. In addition to promoting a uniformly thick coating of the twofluid layers, the presence (or absence) of the plate affects thehomogeneity of the assembly on the surface and the time taken to removethe fluids. That is, in the absence of a cover plate, a “coffee ring”effect is noted with respect to the deposition of the colloidalmaterial, where with the plate, the deposition is more uniform. Also,the presence of the cover plate extends the time it takes for the fluidsto be removed. So as to give an indication of the gross effect, innon-limiting side-by-side experiments, at room temperature, evaporationtimes for uncovered substrates were on the order of 20-25 minutes,whereas covered substrates took between 90 and 120 minutes to dry. At80′C, these times were less than one minute and 10-20 minutes,respectively

The first layer may be removed using several techniques, including bythe application of heat or vacuum or both. In such cases, the firstlayer may be removed by some contribution of evaporation or comminglingwith, and incorporating into, the aqueous phase, or both. Obviously, thecontribution of each potential mechanism depends on the physicalproperties of the first fluid. The skilled artisan would appreciate, forexample, that the contribution by evaporation would be more likely for avolatile, non-polar liquid than it would be for a relativelynon-volatile, water miscible fluid, and that the efficiency of such amechanism would be enhanced by the absence of edge sidewalls adjacent tothe first fluid layer.

Once the first fluid is removed, and the colloidal particles aredeposited, the invention describes that the liquid portion of theaqueous dispersion is removed by the application of heat or vacuum orboth. Generally, the application of heat is referring to temperatures ofabout 99° C. or less, 80° C. or less, about 60° C. or less, about 40° C.or less, or so-call room ambient temperatures (e.g., ca. 20-25° C.). Theskilled artisan will appreciate that higher temperatures will causefaster evaporation, though the speed of evaporation is balanced againstthe homogeneity and/or selectivity he or she wishes to attain.

As described above, additional embodiments include those wherein thecolloidal particles remaining after the removal of the first and secondlayers of liquid form patterned deposits on the substrate. Thesedeposits can be positioned over wide areas, or within constrainedfeatures, such as channels or holes. In some embodiments, the patternedlayer of particles on the substrate form at least one electricalconductor or semiconductor device; e.g., a micro-/nano-wires or diode.In other embodiments, the patterns may comprise particles containingresidual surfactants, ligands, or biopolymers, making them particularlysuitable for sensor applications. In still other embodiments, thepattems may comprise photosensitive or photoactive materials, makingthem suitable for photonic applications. In still other applications,the patterns may comprise magnetic materials, making them particularlysuitable for information storage or transfer applications.

To this point, the various embodiments of this invention have describedmethods for depositing colloidal particles onto a substrate surface.However, it should be appreciated that articles produced by thesemethods are also within the scope of this invention. Such articlesinclude, for example, chemical, biochemical, electrical, electromagneticfield or frequency sensors, information storage media, energy storageunits, energy conversion cells, display devices, or video or opticaldevices. More complicated systems are also contemplated herein,including chemical, biochemical, electrical, or electromagnetic field orfrequency sensing systems, information transfer or communicationsystems, energy storage or conversion systems, or video or opticalcommunication systems comprising a device made by these methods.

As those skilled in the art will appreciate, numerous modifications andvariations of the present invention are possible in light of theseteachings, and all such are contemplated hereby. For example, inaddition to the embodiments described herein, the present inventioncontemplates and claims those inventions resulting from the combinationof features of the invention cited herein and those of the cited priorart references which complement the features of the present invention.Further, to the extent that the descriptions provided for the methods ofimproving the interfacial self-assembly processes are not specificallyreflected in the descriptions for the articles produced by this methods,it should be readily apparent that these are considered to be within thescope of the latter, and vice versa. Similarly, it will be appreciatedthat any described material, feature, or device may be used incombination with any other material, feature, or device, so as toprovide a flexible toolkit of options.

The disclosures of each patent, patent application, and publicationcited or described in this document are hereby incorporated herein byreference, in their entirety.

What is claimed is:
 1. A device comprising: a substrate having a surfacewhich has not been plasma etched, and a plurality of colloidal particlesdeposited on said surface.
 2. The device of claim 1, wherein the deviceis configured as a chemical, biochemical, electrical, electromagneticfield or frequency sensor, an information storage medium, an energystorage unit, an energy conversion cell, a display device, or an opticaldevice.
 3. The device of claim 1, wherein the substrate is hydrophobic.4. The device of claim 1, wherein the substrate is hydrophilic.
 5. Thedevice of claim 1, wherein the substrate comprises a material selectedfrom the group consisting of glass, organic polymer, inorganic polymer,ceramic, metal, metalloid, and layered combinations or mixtures thereof.6. The device of claim 1, wherein the surface is non-metallic and atleast partly metallized.
 7. The device of claim 6, wherein themetallization is lithographically patterned.
 8. The device of claim 5,wherein the substrate comprises glass and the glass comprises asilicate, borate, phosphate, or a combination or mixture thereof.
 9. Thedevice of claim 5, wherein the substrate comprises an organic polymerand the organic polymer comprises a thermoplastic or thermoset resin orcopolymer or mixture thereof.
 10. The device of claim 5, wherein thesubstrate comprises an organic polymer and the organic polymer comprisesa partially or perfluorinated polymer, polycarbonate, polyester,polyalkylene, polyacrylate or polymethacrylate, polystyrene,polyacrylonitrile, or a copolymer or mixture thereof.
 11. The device ofclaim 5 wherein the substrate comprises an organic polymer and theorganic polymer is electrically conductive or semi-conductive.
 12. Thedevice of claim 11, wherein the organic polymer comprisespoly(para-phenylene vinylene), polythiophene, poly(paraphenylene),polyquinoline, polypyrrole, polyacetylene, polyfluorene, or a copolymeror mixture thereof.
 13. The device of claim 5, wherein the substratecomprises an inorganic polymer and the inorganic polymer comprisespolysiloxane, silicate, aluminosilicate, or a combination or mixturethereof.
 14. The device of claim 5, wherein the substrate comprises aceramic and the ceramic comprises a metal or metalloid oxide, nitride,carbide, or a combination or mixture thereof.
 15. The device of claim14, wherein the ceramic comprises aluminum oxide, aluminum nitride,aluminum carbide, titanium oxide, titanium nitride, titanium carbide,silicon oxide, silicon carbide, silicon nitride, boron carbide, boronnitride, antimony oxide, iron oxide, magnesium oxide, nickel oxide, tinoxide, zinc oxide, zirconium oxide, or a combination or mixture thereof.16. The device of claim 5, wherein the substrate comprises a metal andthe metal comprises aluminum, gold, silver, platinum, cadmium, copper,nickel, titanium, or iron, or a combination or mixture thereof.
 17. Thedevice of claim 5, wherein the substrate comprises a metalloid and themetalloid comprises doped or undoped Si, CdS, CdSe, Ge, GaAs, GaAlAs,ZnS, InP, Ge, or a combination or mixture thereof, and wherein thesubstrate is conducting, semiconducting, or insulating.
 18. The deviceof claim 5, wherein the substrate comprises silica, polyethylene, orpolycarbonate.
 19. The device of claim 1, wherein the substratecomprises patterned micro- or nano-dimensioned features.
 20. The deviceof claim 19, wherein the patterned features have aspect ratios of 10 ormore.